Dispensers of the above type are presently available on the market. In these dispensers, the plunger that pushes the product to be dispensed in the direction of the dispensing opening is controlled by a very complicated assembly: The plunger is mounted at the end of a threaded rod, which cooperates with a fixed nut integrally joined with the reservoir that contains the product; the threaded rod is displaceable to rotate by means of a mechanism that converts the action of the user upon the pushbutton of the dispenser into a rotation of slight angular amplitude; the rotation of the threaded rod, which cooperates with the aforementioned fixed nut, is converted into a translation of the rod with respect to the reservoir, by an amplitude that is smaller, the less the rotation of the rod becomes, on the one hand, and the smaller the pitch of the thread of the rod is, on the other. Thus for each action upon the pushbutton of the dispenser, a translation of the plunger by several hundredths of a millimeter is obtained, which is entirely satisfactory for dispensing the product. A dispenser of this type that is usable for a liquid product is described in particular in French Pat. No. 2 555 471.
However, the mechanism, which is disposed between the pushbutton and the plunger, is quite expensive, first because of the number of parts comprising it and second because of the complexity of molding the parts, and finally because of the difficulty of assembling this mechanism. The function of such a mechanism is irreversible; when the plunger gets close to the dispensing opening of the reservoir, it cannot be moved backward for refilling the reservoir, because the only possibility of backward travel would be a reverse screwing of the threaded rod in its nut, which is certainly not within the ability of the user to accomplish. The mechanism of such a dispenser must therefore be considered disposable, since it is not reusable when the reservoir is empty, and the cost for such a mechanism greatly increases the cost price of the dispenser filled with the product to be dispensed. For dispensing cosmetic products, since the total volume of the dispenser must be reduced to permit the user to carry it about easily, for instance in a handbag, the reservoir is necessarily of reduced capacity, and consequently the elevated cost of the mechanism raises the price of a small-capacity package; this is particularly unfavorable at the commercial level.